Method for gas—solid contacting in a bubbling fluidized bed reactor

ABSTRACT

The present invention relates to a method for gas-solid contacting in a bubbling fluidized bed reactor by:
     (a) introducing into a reactor with bed length to bed diameter ratio below about 5.0, a primary gas consisting essentially of reactant(s) of the reaction to be carried out in the bed of solid particles through a primary gas distributor located at the reactor bottom at a superficial gas velocity U p , which is very close or equivalent to the minimum fluidization velocity U mf , required for achieving the incipient fluidization of the solid particles in the bed to obtain an emulsion phase consisting essentially of the solid particles and the primary gas with little or no formation of gas bubbles to achieve incipient fluidization or liquid-like behaviour of fluidizable solid particles;   (b) forming gas bubbles in the incipiently fluidized bed by introducing through a secondary gas distributor located immediately above the primary gas distributor a secondary gas, selected from one of the reactants which is used in excess of that required for the reaction stoichiometry, steam, an inert or a mixture of two or more thereof at a superficial gas velocity, U s , which is related to the superficial velocity of the primary gas such that a ratio of the superficial velocity of the secondary gas to the superficial velocity of the primary gas U s /U p , is in the range from about 0.5 to about 10.0, preferably from about 1 to about 5.

This application is a divisional of application Ser. No. 09/817,744filed on Mar. 26, 2001 now U.S. Pat. No. 6,894,183 claims the benefitthereof and incorporates the same by reference.

FIELD OF THE INVENTION

This invention relates to a method for gas-solid contacting in abubbling fluidized bed reactor. This invention particularly relates to amethod for the improvement of gas-solid contacting in a bubblingfluidized bed reactor, useful for highly exothermic or highlyendothermic or temperature sensitive catalytic or non-catalyticreactions, by avoiding the bypass of reaching gas(es) through gasbubbles.

The method of invention can be used in the chemical, petrochemical andpetroleum industries for carrying out highly exothermic, highlyendothermic or temperature sensitive catalytic or non-catalyticreactions in a bubbling fluidized bed reactor.

BACKGROUND OF THE INVENTION

Fluidization of solid particles by gas is a well-known phenomenon. Whena gas is passed upwards to a bed of fine solid particles, the state ofthe bed depends upon the gas flow rate as follows: At low flow rate gasmerely percolates through the voids between the stationary particles andthe bed is called fixed bed. However, with an increase in the gas flowrate, particles move apart forming expanded bed. With a further increasein the gas flow rate, a point is reached when all the particles are justsuspended in the upward flowing gas and such a bed is referred to as anincipiently fluidized bed or a bed at minimum fluidization. When gasflow rate is increased beyond minimum fluidization, large instabilitiesin bubbling and channeling of gas are observed. At this stage, themovement of particles becomes more vigorous but the bed does not expandmuch beyond its volume at minimum fluidization. Such a bed is referredto as bubbling fluidized bed and it consists of two distinct phases: anon-continuous bubble phase consisting mainly of gas with a very lowconcentration of solid particles carried over by the gas bubbles, and acontinuous emulsion phase consisting of solid particles and gas (Ref J.F. Davidson and D. Harrison in Fluidized Particles, Cambridge UniversityPress, 1963; D. Kunii and O. Lavenspiel in Fluidization Engineering,John Wiley and Sons. Inc., New York, 1969).

Most commercial gas fluidized bed reactors for catalytic andnon-catalytic reaction operate in the bubbling regime as bubblingfluidized beds. In the bubbling fluidized bed reactor, the upward motionof the gas bubbles cause enough mixing of solid particles in theemulsion phase, also called as the dense phase and hence the temperatureis nearly uniform in the entire reactor. This effect of gas bubble isfavourable. However, because of the low concentration of solid particlesin the gas bubbles, there is little reaction within the bubbles.Moreover, the bubbles serve as channels for gases to bypass the solidparticles and leave the reactor more or less unreacted for the catalyticreaction, when the solid particles are catalyst particles, and also forthe non-catalytic reactions, when the solid particles are in particlesin case of thermal non-catalytic reactions e.g. thermal cracking ofnaphtha or with sand or solid reactant in case of non-catalyticgas-solid reactions, e.g. reduction of metal oxides by H2 and/or CO,regeneration of coked catalyst by oxidative treatment.

A number of commercial catalytic and non-catalytic reactions are carriedout in bubbling fluidized bed reactors. Art method for the operation ofbubbling fluidized bed reactor for gas phase catalytic or non-catalyticreaction involve a fluidization of solid particles in the reactor byreacting gas(es) at a superficial velocity which is much higher thanthat requird for anticipant fluidization or minimum fluidization of thesolid particles, the reacting gas in excess for incipient or minimumfluidization passes through the reactor in the form of gas bubbles. Theadvantages of bubbling fluidized bed reactors are liquid like flow ofsolid particles, rapid mixing of solid particles leading nearlyisothermal conditions throughout reactor, possibility or circulatingsolids between two fluidized beds so that catalysts particles coked dueto catalytic reaction in one reactor can be transported to secondreactor or their regeneration by oxidative treatment, high rates of heattransfer between a fluidized bed and a heat exchanger immersed withinfluidized bed. All these advantages make the operation of bubblingfluidized bed reactor simple, easy and reliable from process controlpoint of view. However, disadvantages or limitations of bubblingfluidized bed reactors used earlier are also many. The main limitationof using bubbling fluidized bed reactor for a catalytic or non-catalyticreaction is the difficulty in describing the flow of reacting gasthrough the emulsion phase and bubble phase, with its large deviationfrom plug flow and bypassing of the solid particles by reacting gasthrough gas bubbles, resulting in an inefficient contacting betweensolid particles and reacting gas. This becomes particularly very seriouswhen high conversion of reacting gas is required. Commercial scaleoperations involve high gas throughputs, requiring large bed diametersand gas velocities. Both these factors lead to vigorously bubbling bedswith large size bubbles with their serious bypassing and poor gas-solidcontacting. Under such condition a high conversion can be attained bykeeping contact time long by increasing reactor height for a givenoperating gas velocity at a cost of increased capital, increasedcatalytic cost increasing power requirement for pumping the gas streams.However, high selectivity cannot be achieved by this as it can beachieved only under high gas-solid contact efficiency. Also because ofthe non-ideal flow of the gas in the bubbling fluidized bed reactors andcomplex nature of the exchange of gas between emulsion phase and bubblephase, it is difficult to predict the reactor performance and also todesign or scale-up the reactor (Ref D. Kunii and O. Levenspiel inFluidization Engineering, John Wiley & Sons, Inc. 1969; O. Levenspiel inChemical Reaction Engineering, 2^(nd) Edn. Wiley Eastern Ltd., Y. Ikedain Fluidization on 85: Science and Technology, Ed. Kunii et al,Conference papers, 2^(nd) China-Japan Symposium, Kunming China; SciencePress, Beizing China, Elsevier, Arnst 1985 p.1) and W. Yongan et al,Ibid. p.11).

It is preferable in commercial practice to avoid the bypassing of thereacting gas which is in excess of what required for incipient orminimum fluidization, so that a major limitation or drawback of bubblingfluidized bed reactors could be eliminated. The following are used inthe prior art to overcome the problem of bypassing of reacting gasthrough gas bubbles:

-   (a) Internals are inserted into the bed to hinder gas bubble growth    and also to cut down size of bubbles. This reduces bypassing of    reacting gas through gas bubbles but only to a small extent.-   (b) A combination of bubbling fluidized bed and packed bed reactor,    where the gas first passes through the fluidized bed section and    then through the packed bed section, is used for achieving high    conversion of reacting gases. This reactor system is however,    complex and difficult to operate and control and yet there is a    bypass of reacting gas through bubbles of the bubbling bed reactor.-   (c) A use of fast fluidization with less fluidized solid particles    is also suggested. As compared to bubbling fluidized bed, the fast    or lean fluidized bed has some advantages, such as the gas-solid    contact efficiency is higher and the gas flow is plug or piston    flow. However, it has also a serious drawback such as the solid    particles in the reactor becomes very dilute and the advantages of    bubbling fluidized bed in commercial operation are lost    References: O. Levenspiel in Chemical Reaction Engineering, 2^(nd)    edition, Wiley Eastern Ltd., and Y. Ikeda in Fluidization 1985:    Science and Technology, Ed. Kunii. et. al., Conference papers,    2^(nd) China-Japan Symposium Kunming, China, Science Press, Beijing,    China, Elsevier, Amst., 1985).

If the bypass of reacting gas(es) through gas bubbles in bubblingfluidized bed reactor is eliminated or drastically reduced, and therebygas-solid contacting efficiency is increased, this would be of greatpractical importance for carrying out a number of highly exothermic,highly endothermic catalytic or temperature sensitive non-catalyticreactions, using bubbling fluidized bed reactors. Hence, thee is a needfor developing an improved method for the operation of bubblingfluidized bed reactor to achieve this goal.

OBJECTS OF THE INVENTION

This invention is made with the following objects so that most of thedrawbacks or limitations of the prior art method for the operation ofbubbling fluidized bed reactor for catalytic or non-catalytic reactionscould be overcome.

The main object of the present invention is to eliminate or drasticallyreduce a bypass of reacting gas through gas bubbles without itscontacting with solid particles and thereby to achieve an efficientcontacting between solid particles and reacting gas in a bubblingfluidized bed reactor so that a high conversion of reacting gas(es).

It is another object of the present invention to obtain a highselectivity for gas phase catalytic or non-catalytic reactions inbubbling fluidized bed reactors.

Another object of this invention is to simplify and also make easier thedesign and/or scale-up of a bubbling fluidized bed reactor for catalyticor non-catalytic reactions.

SUMMARY OF THE INVENTION

These and other objects are accomplished in this invention by providinga novel method for the improvement of gas-solid contacting in a bubblingfluidized bed reactor, useful for gas phase catalytic or non catalyticor non-catalytic reaction.

Accordingly the present invention relates to a method for gas-solidcontacting in a bubbling fluidized bed reactor said method comprising:

-   (a) introducing into a reactor with bed length to bed diameter ratio    below about 5.0, a primary gas consisting essentially of reactant(s)    of the reaction to be carried out in the bed of solid particles    through a primary gas distributor located at the reactor bottom at a    superficial gas velocity U_(p), which is very close or equivalent to    the minimum fluidization velocity U_(mf), required for achieving the    incipient fluidization of the solid particles in the bed to obtain    an emulsion phase consisting essentially of the solid particles and    the primary gas with little or no formation of gas bubbles to    achieve incipient fluidization or liquid-like behaviour of    fluidizable solid particles;-   (b) forming gas bubbles in the incipiently fluidized bed by    introducing through a secondary gas distributor located immediately    above the primary gas distributor a secondary gas, selected from one    of the reactants which is used in excess of that required for the    reaction stoichiometry, steam, an inert or a mixture of two or more    thereof at a superficial gas velocity, U_(s), which is related to    the superficial velocity of the primary gas such that a ratio of the    superficial velocity of the secondary gas to the superficial    velocity of the primary gas U_(s)/U_(p), is in the range from about    0.5 to about 10.0, preferably from about 1 to about 5.

In one embodiment of the invention, the direct bypassing of the reactinggas through gas bubbles is avoided using a reacting gas only forobtaining an incipient fluidization without forming gas bubbles, whileretaining the advantages of bubbling fluidized bed reactor.

In another embodiment of the invention, the reactor comprises a singlebubbling fluidized bed reactor or individual bubbling fluidized bedreactors of a multiple reactor system consisting of two or more bubblingfluidized bed reactors with continuous transportation or re-circulationof solid particles between the reactors.

In another embodiment of the invention, the size of the solid particlesin the reactor is below 150 um.

In a further embodiment of the invention, the reaction comprises acatalytic reaction, a non-catalytic thermal reaction or a non-catalyticgas-solid reaction.

In a further embodiment of the invention, the solid particles in thereactor consist essentially of a catalyst useful for catalysing thereaction.

In yet another embodiment of the invention, the catalytic reactionswhich can be carried out using said method comprise ammoxidation ofpropylene or propane to acrylonitrile, oxidation of propylene or propaneto acrolein and/or acrylic acid, oxidation of naphthalene or o-xylene tophthalic anhydride, oxidation of benzene or butane to maleic anhydride,Fischer Tropsch synthesis of hydrocarbons and or oxygenates from carbonmonoxide and hydrogen, gas phase chlorination or oxychlorination ofhydrocarbons, gas phase hydrogenation of organic compounds, fluidcatalyst cracking of oil, fluid catalytic reforming of naphtha and otherhydrocarbons, reforming of hydrocarbons to synthesis gas, hydrocrackingof heavy oil.

In another embodiment of the invention, when said method is used forcarrying out a non-catalytic reaction in a bubbling fluidizing bedreactor, the solid particles in the reactor consist of inert solid, suchas sand, sintered silica, sintered alumina, sintered silica-alumina,sintered zirconia-haffnia or other sintered and/or refractory materialwhich is chemically inert to the reactants of the thermal reactions.

In a further embodiment of the invention, the non-catalytic thermalreactions which are carried out using said method are fluid thermalcracking processes.

In yet another embodiment of the invention, the fluid thermal crackingprocess comprises thermal cracking of naphtha and heavy oil.

In yet another embodiment of the invention, when said method is used forcarrying out a non-catalytic gas-solid reaction in a fluidized bedreactor, the solid particles in the reactor consist essentially of solidreactant, such as reducible metal oxides, partially reduced metaloxides, deactivated catalyst due to coking of other solid reactants ofknown gas-solid reactions, which is converted into product of thereaction.

In a further embodiment of the invention, the non-catalytic gas-solidreactions are selected from reduction of metal oxides from ores inmetallurgical industries, gasification, of coal combustion of coal orregeneration of coked catalyst by gasification of carbon or coke presentin the catalyst.

In a further embodiment of the invention, the size of the fluidizablesolid particles used in the fluidized bed reactor are in the range offrom 30 μm to 150 μm.

In another embodiment of the invention, the primary gas comprises of oneor more reactants of the reaction to be carried out in the reactor.

In a further embodiment of the invention, the ratio of superficialvelocity of secondary gas U_(s), to superficial velocity of primary gasU_(p), is between 1 and 5.

In another embodiment of the invention, the primary and secondary gasesare introduced in the reactor separately, using separate gasdistributors.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The FIG. 1 is a schematic of a bubbling fluidized bed reactor showingthe emulsion phase, bubble phase or gas bubbles in emulsion phase, gasline and distributor for the primary gas, and also gas line anddistributor for the secondary gas.

DETAILED DESCRIPTION OF THE INVENTION

The improvement in the method of the invention for the gas-solidcontacting in a bubbling fluidized bed reactor, useful for gas phasecatalytic or non-catalytic reaction comprises:

-   (a) achieving an incipient fluidization or liquid-like behaviour of    fluidizable solid particles, which are either catalyst particles or    inert solid particles or particles of solid reactant or mixture of    two or more thereof, contained in a reactor with bed length to bed    diameter ratio below about 5.0, by introducing a primary gas    consisting essentially of reactant(s) of the reaction to be carried    out, in the bed of solid particles through a primary gas distributor    located at the reactor bottom at a superficial gas velocity U_(p),    which is very close or equivalent to a minimum fluidization    velocity, U_(mf), required for achieving the incipient fluidization    of the solid particles in the bed, such that an emulsion phase    consisting essentially of the solid particles and the primary gas    with little or non formation of gas bubbles;-   (b) forming gas bubbles in the incipiently fluidized bed by    introducing through a secondary gas distributor located immediately    above the primary gas distributor a secondary gas, selected from one    of the reactants which is used in excess of that required for the    reaction stoichiometry, steam, an inert gas or a mixture of two or    more thereof a superficial gas velocity U_(s), which is related to    the superficial velocity of the primary gas such that a ratio of the    superficial velocity of the secondary gas to the superficial    velocity of the primary gas U_(s)/U_(p), is in the range from about    0.5 to about 10.0

Referring now to FIG. 1 for the method of this invention, the primarygas PG enters the bed of solid particles through primary gas line 2 andprimary gas distributor 3, located at the bottom of the bed, at asuperficial velocity U_(p) equal to or close to be minimum fluidizationvelocity U_(mf) required for fluidizing the solid particles, forming anemulsion phase 1 consisting of the primary gas and the solid particles,and then the secondary gas SG enters the emulsion phase at a superficialvelocity U_(s) which is equal to or higher than the minimum fluidizationvelocity U_(mf), through a secondary gas line 4 and secondary gasdistributor 5, which is located above the primary gas distributor 3,preferably immediately above the primary gas distributor, forming gasbubbles GB or bubble phase in the fluidized solid particles. Cyclone 6traps the solid particles that have escaped the fluidized bed and returnthem back to the fluidized bed via dipleg 7. Fresh solid particles canbe added through the dipleg as shown by line 8 to make-up the particlesthat have been lost as fine particles along with the overhead gases,that leave the reactor through the product gas line 9. The cyclone maybe placed within the reactor vessel or external to the vessel. Multiplecyclones may also be used for separating fine solid particles from theoutgoing overhead gases and returning the separated particles back tothe fluidized bed via diplegs.

The method of the invention has application for operating singlebubbling fluidized bed reactor or individual bubbling fluidized bedreactors of a multiple reactor system consisting of two or more bubblingfluidized bed reactors with continuous transportation or re-circulationof solid particles between the reactors.

Bubbling fluidized bed reactor operated by said method may contain heatexchangers but it may or may not contain reactor internals. The size ofthe solid particles in the reactor may be below 150 um. When the reactoris operated by said method, the presence of vertical and horizontalreactor internals which are used in prior art for breaking large sizegas bubbles or for restricting size of gas bubbles is not essential.

The method of present invention can be used for carrying out catalyticreactions, non-catalytic thermal reactions or non-catalytic gas-solidreactions.

When said method is used for carrying a catalytic reaction in bubblingfluidized bed reactor, the solid particles in the reactor consistessentially of a catalyst useful for catalysing the reaction. Theexamples of catalytic reactions which can be carried out using saidmethod are ammoxidation of propylene or propane to acrylonitrile,oxidation of propylene or propane to acrolein and/or acrylic acid,oxidation of naphthalene or o-xylene to phthalic anhydride, oxidation ofbenzene or butane to maleic anhydride, Fischer Tropsch synthesis ofhydrocarbons and or oxygenates from carbon monoxide and hydrogen, gasphase chlorination or oxychlorination of hydrocarbons, gas phasehydrogenation of organic compounds, fluid catalyst cracking of oil whichis commonly known in FCC process fluid catalytic reforming of naphthaand other hydrocarbons, reforming of hydrocarbons to synthesis gas,hydrocracking of heavy oil, or other exothermic or endothermic catalyticreactions the operations of which are to be restricted within a narrowtemperature range, either because of the explosive nature of thereaction or because of temperature sensitivity of desired product orbecause of product distribution considerations.

When said method is used for carrying out a non-catalytic reaction in abubbling fluidizing bed reactor, the solid particles in the reactorconsist of inert solid, such as sand, sintered silica, sintered alumina,sintered silica-alumina, sintered zirconia-haffnia or other sinteredand/or refractory material which is chemically inert to the reactants ofthe thermal reactions, the role of which is to carry heat and provide itto the reactants of the thermal reaction. The examples of non-catalyticthermal reactions which can be carried out using said method are fluidthermal cracking processes, such as thermal cracking of naphtha andheavy oil and the like.

When said method is used for carrying out a non-catalytic gas-solidreaction in a fluidized bed reactor, the solid particles in the reactorconsist essentially of solid reactant, such as reducible metal oxides,partially reduced metal oxides, deactivated catalyst due to coking ofother solid reactants of known gas-solid reactions, which is convertedinto product of the reaction. The examples of non-catalytic gas-solidreactions are reduction of metal oxides from ores in metallurgicalindustries, gasification, of coal combustion of coal, regeneration ofcoked catalyst by gasification of carbon or coke present in the catalystand the like.

The size of the fluidizable solid particles used in the fluidized bedreactor normally range from about 30 um to about 150 um.

In the method of this invention, the primary gas consists essentially ofone or more reactants of the reaction to be carried out in the reactorand its role is to provide a minimum or incipient fluidization of solidparticles in the reactor as far as possible without forming gas bubblesand thereby making the bed of solid particles fluid-like and alsoprovide reactant(s) for the reaction in the reactor. In the method ofthis invention, a small number primary gas bubbles may be formed but itis preferable if no gas bubble of the primary gas is formed in thereactor.

In the method of this invention, the main role of the secondary gas isto form gas bubbles in the incipiently fluidized bed of solid particlesand, thereby, to mix the solid particles in the reactor so that auniform or isothermal temperature through out the reactor can bemaintained. The other role of the secondary gas is to remove heat fromor provide heat to the solid particles in the reactor. The secondary gasmay also provide a reactant for the reaction(s) in the reactor.

In the method of this invention, the preferred ratio of superficialvelocity of secondary gas U_(s), to superficial velocity of primary gasU_(p), is between 1 and 5.

In the method of this invention, the primary and secondary gases areintroduced in the reactor separately, using separate gas distributors.The gas distributor used for distributing the primary gas is located atthe reactor bottom and the gas distributor used for distributing thesecondary gas is located above the distributor used for the primary gas.Different types of gas distributors are known in the prior art (Ref D.Kunii and O. Levenspiel in Fluidization Engineering, John Wiley & Sons,Inc., New York, 1969).

For avoiding bypassing of the reacting gas(es) and thereby achieving anefficient gas-solid contacting in a bubbling fluidized bed by the methodof this invention, it is preferable to introduce the primary gas at thebottom of the bed of the solid particles as uniformly as possible byusing a suitable gas distributor known in the prior art and it is alsopreferable to introduce the secondary gas in form of large bubbles inthe fluidized solid particles using a gas distributor consisting ofsingle or few gas distribution nozzles or bubbles caps. Larger the sizeof the secondary gas bubbles, lesser is the exchange of gases betweenthe emulsion phase and the bubble phase and hence better would be theperformance of the bubbling fluidized bed reactor when operated by themethod of this invention.

By using the method of this invention, highly exothermic, highlyendothermic or temperature sensitive gas catalytic reaction, gas phasenon-catalytic thermal reaction or non-catalytic gas-solid reaction ca becarried out in a bubbling fluidized bed reactor with high conversion andselectivity.

The invention is described with respect to the following examplesillustrating the method of this invention for operating a bubblingfluidized bed reactor for carrying out catalytic or non-catalyticreactions. These examples are provided for illustrative purpose only andare not to be construed as limitations on the method of this invention.

EXAMPLES

Definition of Terms

Superficial gas velocity: It is defined as a ratio of volumetric gasflow rate to cross sectional area of the bed of solid particles. U_(p)and U_(s) are the superficial velocities of the primary and secondarygas, respectively.

Incipiently fluidized bed: When gas flows through solid particlespresent in the reactor, a pressure drop across the bed of solidparticles is developed and when this pressure drop is sufficient tosupport the weight of the particles, the bed is said to be incipientlyfluidized. In incipiently fluidized bed, all the particles in thereactor are suspended with formation of little or no gas bubbles and thebed of suspended particles behaves like a liquid.

Incipient or minimum fluidization velocity U_(m): It is a superficialgas velocity at which solid particles in the reactor are incipientlyfluidized. This velocity can be determined experimentally or estimatedtheoretically by the well known methods described earlier (Ref D. Kuniiand O. Levenspiel in Fluidization Engineering, John Wiley & Sons, Inc.,New York, 1969).

Bubble phase: It is a discontinuous phase formed by the bubbles offluidizing gas, which is the secondary gas, in the method of thisinvention.

Emulsion Phase: It is a continuous dense phase, formed by the solidparticles and the fluidizing gas, which is the primary gas in the methodof this invention.

All the ratios of the chemicals or gases in the examples are moleratios.

Example 1

This example illustrates the method of this invention for operating abubbling fluidized bed reactor for the catalytic vapor phasehydrogenation of nitrobenzene to aniline.

The catalytic reaction can be carried out in a conventional fluidizedbed reactor having an inner diameter of 20 cm and height of 50 cm andcontaining 10 1 50±10 micron size particles of a copper catalyst (25 wt% Cu) supported on silica gel. The catalyst particles can be prepared byimpregnating copper nitrate from its aqueous solution on 50±10 micronsize spherical particles of silica gel followed by drying and calciningand reducing by hydrogen. The temperature in the reactor can becontrolled by providing heat exchange tubes through which a heatexchange fluid is circulated. A primary gas stream, which in this caseis a mixture of hydrogen and vapors of nitrobenzene with ahydrogen/nitrobenzene more ratio of 4.0 can be introduced into thereactor continuously through a gas distributor, called primary gasdistributor, which is located a the bottom of the reactor, as shown inFIG. 1, at a superficial velocity equivalent to the incipientfluidization or minimum fluidization velocity U_(mf), required forsuspending all the catalyst particles in the reactor. The minimumfluidization of the primary gas can be obtained by increasing thesuperficial velocity of the primary gas and observing the increase inthe pressure drop across the catalyst bed in the reactor. Initially withincrease is superficial velocity, a linear increase in the pressure dropacross the catalyst bed is observed until the minimum fluidizationvelocity is obtained. After obtaining the minimum fluidization velocity,the increase in the pressure drop with the increase in the velocity ismuch smaller.

Immediately after attaining the minimum fluidization velocity of theparticles by the primary gas stream, a secondary gas, which in this caseis pure hydrogen can be introduced in the incipient fluidized catalystbed through a single nozzle gas distributor, called secondary gasdistributor, located in the reactor immediately above the primary gasdistributor as shown in FIG. 1, at a superficial gas velocity which isfour times the superficial velocity of the primary gas, forming gasbubbles in the fluidized bed reactor and therefore providing a vigorousmixing of the catalyst particles in the reactor. The hydrogenation ofnitrobenzene occurs in the emulsion phase according to thestoichiometric reaction:C6H5NO2+3H2−→C6H5NH2+2H2O

The reaction can be allowed to occur in the fluidized bed reactor at atemperature of 270±10° C. and about 2 atm. Pressure-with conversion ofnitrobenzene much higher than that could have been obtained whenoperating the bubbling fluidized reactor by introducing all the hydrogengas along with nitrobenzene vapors through the primary gas distributoralone as in case of the conventional operation of the bubbling fluidizedbed reactor.

Simple calculations show that the hydrogen/nitrobenzene mole ratio inthe emulsion and bubble phase are 4.0 and ∞ when the bubbling fluidizedbed reactor is operated as above by the method of this invention.Whereas, the hydrogen/nitrobenzene mole ratio in both the emulsion aswell as bubble phase of the bubbling fluidized bed reactor is 24.0 whenthe reactor is operated by introducing all the feed gases through theprimary gas distributor alone as in the case of the conventionaloperation of the bubbling fluidized bed reactor. When the bubblingfluidized bed reactor for the hydrogenation of nitrobenzene is operatedas the method of this invention, the concentration of nitrobenzene inthe hydrogen—nitrobenzene mixture in the emulsion phase is much greater(by a factor of 6.25) and hence the reaction rate and consequently theconversion nitrobenzene to aniline is expected to be much higher. Alsosince the limiting reactant, nitrobenzene, is mostly in the emulsionphase, and the concentration of the catalyst is much higher in theemulsion phase than that in the bubble phase, which consists essentiallyof hydrogen, the reacting gas-catalyst contacting is much better thanthat when all the feed gases are passed through the primary distributoras in case of the conventional bubbling fluidized bed reactor. Moreover,since most of the reaction can be made to occur in the emulsion phase,the problems with the scale-up and modeling of the bubbling fluidizedbed reactor for accounting the by-passing of the reacting gas throughthe bubble phase and the exchange of gas(es) between the bubble phaseand emulsion phase are eliminated, when the bubbling fluidized bedreactor is operated by the method of this invention.

Example 2

The method of this invention can be used for the vapour phasehydrogenation of ortho-nitrotoluene to ortho-toluidine, using the samereactor and procedure described in Example-1, except that nitrobenzeneis replaced by ortho-nitrotoluene.

Example 3

The method of this invention can be used for the vapor phasehydrogeneration of para-nitrotoluene to para-toluidine, using the samereactor and procedure described in Example 2, except thatortho-nitrotoluene is replaced by para-nitrotoluene.

Example 4–18

The method of this invention can be used for operating a bubblingfluidized bed reactor for several other catalytic or non-catalyticchemical processes listed in Table 1, by the procedure same as thatdescribed in Example 1, except the solid particles, composition ofprimary gas, composition of secondary gas and operating condition of therespective processes, given in Table 1. In these examples size of thesolid particles, composition of primary gas, composition of secondarygas and operating condition of the respective processes, given inTable 1. In these examples size of solid particles may range from 40 umto 120 μm and the bed length to bed diameter ratio may be between 1 and4.

It is well known in the prior art that in case of bubbling fluidized bedreactor, gas excess of that required for the minimum fluidization formsbubbles in the fluidized bed and also that solid particles in theemulsion phase are well-mixed and the gas-flow in the reactor is a plugflow. Hence, when the bubbling fluidized bed reactor is operated by themethod of this invention, as described in the above examples, there islittle or no bypass of the reactants, particularly the limiting reactantthrough the gas bubbles and thereby very drastically improving a contactbetween the reacting gas and solid particles. Since the catalyticreaction occurs mainly in the emulsion phase, the scale up and themodeling of the reaction system is expected to be accomplished much moreeasily than that when the bubbling fluidized bed reactor is operated bythe conventional method used in the prior art.

TABLE 1 Examples of the use of the method of this invention for carryingout different catalytic and non-catalytic processes in a bubblingfluidized bed reactor. Example 4 Example 5 Example 6 Process Partialoxidation of Oxy-steam reforming of Oxy-CO₂ reforming of methane tosynthesis gas methane to synthesis gas methane to synthesis gas (amixture of H₂ and CO) Solid particles Supported Ni catalyst of Same asExample 4 Same as Example 4 60 ± 10 μm size Primary gas Mixture of CH₄and O₂ Mixture of CH₄, O₂ and Mixture of CH₄, O₂ and with CH₄/O₂ moleratio of steam with CH₄:O₂:steam = CO₂ with CH₄:O₂:CO₂ = 1:9 2.0:1.0:0.42.0:1.0:0.4 Secondary gas Steam Steam Steam Operating ConditionsU_(p)/U_(mf) ratio 1.0 1.0 1.0 U_(s)/U_(p) ratio 4.0 1.0 2.0 Temperature(° C.) 800–900 800–900 800–900 Pressure (atm) >1.0 >1.0 >1.0 Gas in theemulsion Mixture of mainly CH₄ Mixture of mainly CH₄ Mixture of mainlyCH₄ and phase and O₂ and O₂ and steam O₂ and CO₂ Main reactions in theCH₄ + 0.5 O₂ → CO + H₂ CH₄ + 0.5 O₂ → CO + H₂ CH₄ + 0.5 O₂ → CO + H₂emulsion phase CH₄ + H₂O

CO + 3H₂ CH₄ + CO₂ → 2CO + 2H₂ CO + H₂O

CO₂ + H₂ CO₂ + H₂

CO + H₂O Gas in the bubble Mainly steam Mainly steam Mainly steam phaseExample 7 Example 8 Example 9 Process Oxy-CO₂-steam reformingAmmoxidation of Ammoxidation of of methane to synthesis propylene toacrylonitrile propylene to acrylonitrile gas Solid particles Same asExample 4 Commercial propylene Same as that in Example 8 ammoxidationcatalyst Primary gas Mixture of CH₄, O₂ Mixture of C₃H₆, NH₃ Mixture ofC₃H₆, NH₃ and and CO₂ and steam with and O₂ with air with C₃H₆:NH₃:airmole CH₄:O₂:CO₂:steam = C₃H₆:NH₃:O₂ mole ratio = ratio = 1.0:1.0:102.0:1.0:0.2:0.2 1.0:1.0:1.5 Secondary gas Steam Air Steam OperatingConditions U_(p)/U_(mf) ratio 1.0 1.0 1.0 U_(s)/U_(p) ratio 2.0 3.0–5.02.0 Temperature (° C.) 800–900 400–500 400–500 Pressure (atm) >1.0 2.02.0 Gas in the emulsion Mixture of mainly CH₄ Mixture of mainly C₃H₆,Mixture of mainly C₃H₆, phase and O₂, CO₂ and steam NH₃ and O₂ NH₃ andair Main reactions in the CH₄ + 0.5 O₂ → CO + 2 H₂ C₃H₆ + NH₃ + 1.5 O₂ →Same as in Example 8 emulsion phase CH₄ + CO₂ → 2CO + 2H₂ CH₂═CHCN +3H₂O CH₄ + H₂O → CO + 3H₂ Gas in the bubble Mainly steam Mainly airMainly steam phase Example 10 Example 11 Example 12 Process Ammoxidationof Ammoxidation of Oxidation of propylene to propylene to acrylonitrilepropylene to acrylonitrile acrolein Solid particles Same as that inExample 8 Same as that in Example 8 Bismuth molybdate containingcatalyst Primary gas Same as that in Example 8 Same as that in Example 9Mixture of C₃H₆ and air with C₃H₆:air mole ratio = 1.0:6.0 Secondary gasMixture of steam and air Same as that in Example Steam with steam:airmole ratio = 10 1:1 Operating Conditions U_(p)/U_(mf) ratio 1.0 1.0 1.0U_(s)/U_(p) ratio 5.0 5.0 3.0 Temperature (° C.) 400–500 400–500 350Pressure (atm) 2.0 2.0 2.0 Gas in the emulsion Same as that in Example 8Same as that in Example 9 Mixture of mainly C₃H₆ phase and air Mainreactions in the Same as that in Example 8 Same as that in Example 8C₃H₆ + O₂ → emulsion phase CH₂═CHCHO + H₂O Gas in the bubble Mainly amixture of steam Same as that in Example Mainly steam phase and air 10Example 13 Example 14 Example 15 Process Oxidation of acrolein toRegeneration of coked Regeneration of coked acrylic acid FCC catalystFCC catalyst Solid particles Mixed Co—Mo—Mn oxides Coked FCC catalystCoked FCC catalyst catalyst Primary gas Mixture of acrolein and airMixture of air and steam Same as that in Example with acrolein:air molewith air:steam mole ratio 14 ratio = 1:3 of 1:2 Secondary gas SteamSteam Air Operating Conditions U_(p)/U_(mf) ratio 1.0 1.1 1.0U_(s)/U_(p) ratio 3.0 2.0 4.0 Temperature (° C.) 290 500–600 500–600Pressure (atm) 3.0 1–2 1–2 Gas in the emulsion Mixture of acrolein andair Mainly mixture of air and Mainly mixture of air and phase steamsteam Main reactions in the CH₂═CHCHO + 0.5 O₂ → Coke + O₂ → CO₂ andSame as that in Example emulsion phase CH₂═CHCOOH + H₂O water 14 ΔH =−254 kJ. mol⁻¹ Gas in the bubble Mainly steam Mainly steam Mainly airphase Example 16 Example 17 Example 18 Process Oxychlorination of ethaneFischer Tropsch synthesis Hydrocracking of oil Solid particles Cu²⁺-exchanged NaY Pottasium promoted iron Pd/ultra stable Y zeolite zeolite(U.S. Pat. No. 3987118) catalyst Primary gas Mixture of ethane, oxygenMixture of CO and H₂ Mixture of heavy oil and and HCl with CO:H₂ moleratio of H₂ 1:1.5 Secondary gas Air Steam Hydrogen Operating ConditionsU_(p)/U_(mf) ratio 1.0 1.0 1.0 U_(s)/U_(p) ratio 3.0 1.0 1.5 Temperature(° C.) 300–450 320 300–400 Pressure (atm) 1–2 15–20 10 Gas in theemulsion Mixture of ethane, oxygen Mixture of CO and H₂ Mixture of oiland H₂ phase and HCl Main reactions in the C₂H₆ + HCl + O₂ → CO + H₂ →liquid Oil + H₂ → lighter emulsion phase Clhorinated ethane such ashydrocarbons hydrocarbons 1,2 dichloroethane, 1,2, dichloro-ethylene,1,2, dichloroethane, trichloroethylene, perchloroethylene and vinylchloride Gas in the bubble Air steam Hydrogen phaseThe main novel features and advantages of the method of presentinvention over the prior art method of operating bubbling fluidizedreactors are as follows:

-   1. In the prior art method for the operation of bubbling fluidized    bed reactor for gas phase catalytic or non-catalytic reactions, both    the emulsion and bubble phases in the reactor are formed by a    gaseous fed comprising of reacting gas(es) and hence thee is serious    problem of bypass of a large part of reacting gas(es), without its    contacting with solid particles present in the reactor, through the    gas bubbles. Whereas in the method of present invention, emulsion    phase or incipiently fluidized bed of solid particles is formed by    reacting gas(es), called primary gas, and gas bubbled are formed by    a gas other than the primary gas and hence there is no direct bypass    of reacting gas through gas bubbles; only a small part of reacting    gas(es), which is transferred from emulsion phase to bubble phase    during the formation and rise of bubbles is bypassed.-   2. In case of the prior art method, there is a poor or inefficient    contacting between reacting gas(es) and solid particles in a    bubbling fluidized bed reactor and hence it is possible to achieve    high conversions of reacting gas(es) for a given operating    superficial gas velocity only when the bed length to bed diameter    ratio in the reactor is high, thus requiring larger volume of solid    particles, larger reactor and consequently higher capital cost and    also larger pumping cost due to the increased pressure drop across    the bed. On the contrary, incase of the method of present invention,    most of the reacting gas(es) is present in emulsion phase and hence    there is an efficient contacting between reacting gas(es) and solid    particles in bubbling fluidized bed reactor, and thereby, it is    possible to achieve high conversion of reaching gas(es) in catalytic    or non-catalytic reactions even in a shallow bubbling fluidized bed    reactor having a low bed length to bed diameter ratio.-   3. In case of the prior art method, the flow pattern of reacting    gas(es) in the bubbling fluidized bed reactor is complex, not well    known, and also with considerable bypassing, as the reaching gas    flows through both the emulsion and bubbles phases with some    exchange of gas between the two phases and, therefore the flow    pattern which will develop, the degree of contacting between    reacting gas(es) and solid particle and the conversion of reacting    gas(es) in the reactor performance can not be predicted with    assurance. Because of this, the design and scale-up of bubbling    fluidized bed reactor are difficult and also unreliable. Whereas    when the reactor is operated by the method of present invention, the    contacting between reacting gas(es) and solid particles is efficient    and the flow pattern, particularly of reacting gas(es), in the    reactor can be predicted with assurance. All these simplify the    design or scale up of the reactor and also make it reliable.-   4. In case the prior art method, internals in the reactor are    essential for breaking large size bubbles, and thereby, avoiding    some bypass of reacting gas. Whereas in case of the method of this    invention, thee is no need to break large size bubbles and hence    reactor internals are not essential and this reduces the capital    cost and other complications created by reactor internals.

1. A method for carrying out a reaction selected from oxidation of propylene or propane to acrolein and/or acrylic acid, oxidation of naphthalene or o-xylene to phthalic anhydride, oxidation of benzene or butane to maleic anhydride, Fischer Tropsch synthesis of hydrocarbons and or oxygenates from carbon monoxide and hydrogen, gas phase clorination or oxychlorination of hydrocarbons, gas phase hydrogenation of organic compounds, fluid catalyst cracking of oil, fluid catalytic reforming of naphtha and other hydrocarbons, reforming of hydrocarbons to synthesis gas, hydrocracking of heavy oil by effecting gas-solid contact in a bubbling fluidized bed reactor said method comprising: (a) introducing into a reactor with bed length to bed diameter ratio below about 5.0, a primary gas consisting essentially of reactant(s) of the reaction to be carried out in the bed of solid particles through a primary gas distributor located at the reactor bottom at a superficial gas velocity U_(p), which is very close or equivalent to the minimum fluidization velocity U_(mf), required for achieving the incipient fluidization of the solid particles in the bed to obtain an emulsion phase consisting essentially of the solid particles and the primary gas with little or no formation of gas bubbles to achieve incipient fluidization or liquid-like behaviour of fluidizable solid particles; (b) forming gas bubbles in the incipiently fluidized bed by introducing through a secondary gas distributor located immediately above the primary gas distributor a secondary gas, selected from one of the reactants which is used in excess of that required for the reaction stoichiometry, steam, an inert or a mixture of two or more thereof at a superficial gas velocity, U_(s), which is related to the superficial velocity of the primary gas such that a ratio of the superficial velocity of the secondary gas to the superficial velocity of the primary gas U_(s)/U_(p), is in the range from about 0.5 to about 10.0.
 2. A method as claimed in claim 1, wherein the direct bypassing of the reacting gas through gas bubbles is avoided using a reacting gas only for obtaining an incipient fluidization without forming gas bubbles, while retaining the advantages of bubbling fluidized bed reactor.
 3. A method as claimed in claim 1, wherein the reactor comprises a single bubbling fluidized bed reactor or individual bubbling fluidized bed reactors of a multiple reactor system consisting of two or more bubbling fluidized bed reactors with continuous transportation or re-circulation of solid particles between the reactors.
 4. A method as claimed in claim 1, wherein the size of the solid particles in the reactor is below 150 um.
 5. A method as claimed in claim 1, wherein the reaction comprises a catalytic reaction, a non-catalytic thermal reaction or a non-catalytic gas-solid reaction.
 6. A method as claimed in claim 5, wherein the solid particles in the reactor consist essentially of a catalyst useful for catalysing the reaction.
 7. A method as claimed in claim 1, wherein when said method is used for carrying out a non-catalytic reaction in a bubbling fluidizing bed reactor, the solid particles in the reactor consist of inert solid, such as sand, sintered silica, sintered alumina, sintered silica-alumina, sintered zirconia-haffnia or other sintered and/or refractory material which is chemically inert to the reactants of the thermal reactions.
 8. A method as claimed in claim 7, wherein the non-catalytic thermal reactions which are carried out using said method are fluid thermal cracking processes.
 9. A method as claimed in claim 8, wherein the fluid thermal cracking process comprises thermal cracking of naphtha and heavy oil.
 10. A method as claimed in claim 1, wherein when said method is used for carrying out a non-catalytic gas-solid reaction in a fluidized bed reactor, the solid particles in the reactor consist essentially of solid reactant, such as reducible metal oxides, partially reduced metal oxides, deactivated catalyst due to coking of other solid reactants of known gas-solid reactions, which is converted into product of the reaction.
 11. A method as claimed in claim 10, wherein the non-catalytic gas-solid reactions are selected from reduction of metal oxides from ores in metallurgical industries, gasification, of coal combustion of coal or regeneration of coked catalyst by gasification of carbon or coke present in the catalyst.
 12. A method as claimed in claim 1, wherein the size of the fluidizable solid particles used in the fluidized bed reactor are in the range of from 30 pm to 150 gm.
 13. A method as claimed in claim 1, wherein the primary gas comprises of one or more reactants of the reaction to be carried out in the reactor.
 14. A method as claimed in claim 1, wherein the ratio of superficial velocity of secondary gas U_(s), to superficial velocity of primary gas U_(p), is between 1 and
 5. 15. A method as claimed in claim 1, wherein the primary and secondary gases are introduced in the reactor separately, using separate gas distributors. 